Electrostatic lens



March 22, 1960 E. GUNDERT 2,929,948

ELECTROSTATIC LENS Filed May 17, 1954 H I i 3 f i! I} 5 INVENTOR. E am HARD gu/mek 7- ilnited States Patent ELECTROSTATIC LENS Eberhard Gundert, Ulm, Danube, Germany,'assignor to Telefunkeu Gesellschaft fuer draktlose Telegraphic m.b.H., Hannover, Germany The present invention relates to a new and improved unipotential -or accelerating electrostatic lens arrangement.

It is an object of the present invention to provide an electrostatic lens arrangement which is so constructed that the possibility of corona discharge and consequent impairment of the efliciency of the lens is substantially lessened.

A further object of the invention is an electrostatic lens arrangement with one tubular inner electrode 8 or 9 which has a body portion 1 or 2 and an outwardly flaring end portion or 4, an outer tubular lens electrode 3 which is arranged coaxially with said inner electrode 8 or 9 and encloses at least the outwardly flaring end portion 5 or 4; furthermore the arrangement may also comprise further electrodes of the conventional manner. This type of construction substantially increases the distance between the ends 6-6 of the outer lens electrode 3, from which ends the corona discharge normally takes place, and the inner electrode 8 or 9, so that the possibility of corona discharge is substantially lessened. In operation of the arrangement above, the inner electrode 8 or 9 is normally maintained at a high value of positive potential and the outer lens electrode is made negative with respect thereto.

Another object of the invention is an electrostatic lens arrangement which is provided with a pair of tubular, axially aligned, inner electrodes, each of which has a body portion and an outwardly flaring portion, the end portions being located opposite and spaced from one another. An outer tubular lens electrode is arranged coaxially with said inner electrodes and en closes the space between the outwardly flaring end portions of the inner electrodes and the outwardly flaring end portions themselves. This type of construction substantially increases the distance between the opposite ends of the lens electrode, fromwhich ends corona discharge normally takes place, and the respective inner electrodes so that the possibility of corona discharge is substantially lessened.

In preferred embodiments of the invention the outwardly flaring portions of the inner electrode may be conically or flange-shaped. Also, in a preferred embodiment of the invention the edge portions of the lens electrode are rounded and made of increased crosssectional configuration as, for example, by bending these edge portions inwardly so as to form raised, rounded inner ridges at the respective opposite ends of the lens electrode.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing which is a crossefiiciency of the lens arrangement.

ice

sectional view of an electrostatic lens arrangement in accordancewith the invention.

Referring now to the drawing there is shown a first inner electrode Shaving a hollow, cylindrical body portion 1 and an'outwardly flaring, conically-shaped end portion 5, anda second inner electrode 9, axially aligned with electrodelS, having a hollow, cylindrical body portion 2 and a circular, flange-shaped, outwardly-flaring end portion 4. Surrounding the two inner electrodes is a lens electrode 3, the edges of the opposite end portions of which are bent inwardly to form a pair of rounded, inwardly-extending ridges 6. The twoinner electrodes are maintained at the same potential by -a conductive connection 7 connecting the two together, as shown at the left of the drawing. i

In operation of the arrangement above, the inner electrodes are normally maintained at a high valueof positive potential and the outer lens electrode is made negative with respect thereto. The inner electrodes, for example, may be maintained at a potent-ial of 15 kilovolts and the lens electrode at a potential of about 200 volts. Optimum operation is achieved by causing the opposite ends of the inner electrodes to flare outwardly so that the edges of the inner electrodes are relatively widely spaced from an electron beam which is desired to focus. This would normally result in an increase in corona discharge between the lens electrode and the inner electrodes because the spacing between these] outwardly flaring edges and the opposite edge portions of the lens electrode would be considerably reduced. Such corona discharge would, of course, impair the This tendency is counteracted by making the lens electrode of sufiicient length completely to' enclose the flaring end portions of the inner electrodes so that the edges of the relatively negative lens electrode from which corona discharge normally is initiated, are relatively widely spaced from the body portions of the respective inner electrodes. Rounding the edges of the lens electrode fur ther lessens the possibility of corona discharge.

The above-described arrangement is particularly advantageous for use with a cathode ray tube beam focusing arrangement and other types of electron beam sys terns. The'len-s arrangement is, of course, arranged so that the electron beam passes through the axially aligned hollow cylindrical inner electrodes 8 and 9.

In theembodiment of the invention illustrated, one of the flaring end portions of the inner electrode is shown as being conically-shaped, and the other flaring end portion as being flange-shaped. It is to be understood, however, that the invention is equally applicable to the case in which both flaring end portions are conically-shaped or in which both flaring end portions are flange-shaped. It is to be further understood that other shapes beside conical and flange shapes may advantageously be employed for the inner electrode ends. Finally, it is to be understood that the inner ridges 6 at the cpposite ends of the lens electrode may be formed by means other than bending the edges of the lens inwardly as illustrated in the drawing. For example, ridges 6 may be formed by conductively securing to the opposite edges of the lens electrode independent rounded metal portions.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electrostatic lenses diflering from the types described above.

While the invention has been illustrated and described as embodied in electrostatic lenses especially suitable for use in a cathode ray tube, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departingin way from spirit of the present invention.

Without further analysis; the foregoing will so fully reveal the gist of the present invention thatotherscan by "applying currentknowledge" readily adapt: 'it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects-of this invention and, therefore, such adaptations should and arefintended to be comprehended within the meaning and range of equivalence of the following clairn.

- What is claimed as new and desired to be secured by Letters Patent is:

An electrostatic lens arrangement comprising, in combination, a pair of hollow cylindrical, axially aligned, inner electrodes, each of saidelectrodes having a body portion and an outwardly flaring end portion, said end portions being located opposite and spaced from each other, at least one of said flaring end portions being 'e'oni'cally shaped; and an outer, tubular lens electrode arranged coaxially with said inner electrodes having a diameter greater thansaid outwardly flaring end portions of said inner electrode, said outer lens electrode enclosing the space between saidoutwardly flaring end portions and at least said outwardly flaring end portions theinselves, the edges of the opposite ends ot said lens electrode being bent inwardly so as to form a pair of rounded inwardly extending ridges at the respective opposite ends of said lens electrode, said last-named configuration resulting in a lessening of the possibility of corona discharge from said opposite ends of said outer lens electrode, said opposite ends of said outer lens electrode being relatively widely spaced from the respective body portions of said inner electrodes, and the danger of corona discharge from said opposite ends to the respective inner electrodes when said outer lens electrade is maintained at a potential which is substantially more negative than that of said inner electrodes is substantially' lessened. r I

ReferencesCited in the file of this patent UNITED STATES PATENTS 

